Summary An Air Canada Boeing 737 (ACA3697) was en route from Winnipeg International Airport, Manitoba, to Calgary International Airport, Alberta, at flight level (FL) 350. A Canadian Regional Airlines Fokker F28 (CDR8510) departed Calgary en route to Regina International Airport, Saskatchewan, and was climbing to FL290 in a direction opposite to ACA3697. Both flights were in radar coverage under air traffic control. When ACA3697 was about 25nautical miles east of the Empress VOR (VHF omnidirectional radio range), an air traffic controller cleared the aircraft to descend to FL290. After ACA3697 crossed the Empress VOR, the controller, to provide separation from another aircraft, instructed ACA3697 to maintain a heading that was nearly reciprocal that of CDR8510. When the two aircraft were about 6nautical miles apart, a traffic alert and collision-avoidance system resolution advisory instructed CDR8510 to descend, which they did. The two aircraft passed with about 1000feet horizontal and 1300feet vertical spacing in an area where the required minimum separation was 5nautical miles horizontally or 1000feet vertically. Ce rapport est galement disponible en franais. Other Factual Information The aircraft were flying through the Alsask sector in the Calgary en route specialty. The specialty, situated in the Edmonton Area Control Centre (ACC), comprises six sectors. The Alsask sector is on the eastern boundary adjoining airspace controlled by Winnipeg ACC. For flights inbound to Calgary from the east, aircraft are issued descent to 12000feet and the appropriate standard terminal arrival routing (STAR). After departure from Calgary, CDR8510 was established on Airway J504 eastbound on a track of 073 magnetic and cleared to flight level (FL) 250 while in Calgary Terminal Control airspace. Upon making contact with the Alsask controller at 1100 mountain daylight time,1 CDR8510 was cleared to climb to their flight-planned altitude of FL290. ACA3697 was cleared to proceed westbound at FL350 on Airway J504 to the Empress VOR (VHF omnidirectional radio range) (YEA), Airway J476 to the ALOMO intersection, and then to the Calgary airport via a published STAR. When ACA3697 was about 25nautical miles (nm) east of YEA, the Alsask controller cleared the aircraft to descend to FL290 in preparation for handing control of the flight over to the Calgary terminal sector of Edmonton ACC. After crossing YEA, ACA3697 turned right on J476 in accordance with the clearance. (SeeFigure1.) Figure1. Risk of collision between CDR8510 and ACA3697 When ACA3697 was issued descent clearance, an Airbus A320 (ACA579) was westbound on a track of 252 at FL310 about 11 nm north of YEA. After determining ACA579's heading, the Alsask controller instructed ACA3697 to turn left to a heading of 250, followed shortly by instructions to turn right to a heading of 270. This manoeuvring assured separation between ACA3697 and ACA579, but placed ACA3697 on a track nearly reciprocal to CDR8510. ACA3697 leveled at FL290 approximately 5.9nm in front of CDR8510, which was climbing through FL280 for FL290. While climbing through FL280, CDR8510 received a traffic alert and collision-avoidance system (TCAS) resolution advisory (RA) to descend for traffic avoidance. Within 30seconds, CDR8510 had descended to FL277, passing under ACA3697 at FL290. ACA3697 received a TCAS traffic advisory-information to assist the flight crew visually acquire conflicting traffic and to alert pilots of the possibility of an RA; the pilot took no evasive action. The sky was clear with unlimited visibility, and both flight crews had visual contact with the other aircraft when they passed. Aircraft flying in Canada are not required to be fitted with an on-board collision-avoidance system. The radar data-processing system situational display (RSiT) includes a number of features that assist a controller in maintaining situational awareness. A controller normally tags radar targets with a number of parameters, including aircraft identity, altitude, and speed. S/he can select a halo2 around a particular aircraft target to represent horizontal separation minima. A projected track line (PTL) presents a controller with information on the predicted path that an aircraft will follow for a selected period of time. As an aircraft track changes, the PTL continually changes to indicate the revised track that the aircraft will fly. The PTL can be either displayed or suppressed for each radar target. The controller had selected a PTL for ACA3697 but not for CDR8510. When the controller instructed ACA3697 to turn to a heading of 250, its PTL intersected the target for CDR8510. However, the controller did not detect the conflict. Range halos were not selected for any of the aircraft involved in the incident. Flight progress strips were available and showed direction of flight, altitude, and appropriate marks indicating that the estimates had been passed to concerned sectors. The controller had passed all relevant information about CDR8510 to Winnipeg ACC, including the estimated time at YEA and the aircraft's flight-planned altitude of FL290. The RSiT system has been operational at Edmonton ACC since 2000. All controllers were given a two-day course in its use, and recurrent training is provided when the system is upgraded. The controller involved in this incident received his initial RSiT training in 2000, recurrent training in April2001, and was considered to be competent using the display system. The controller, who was licensed and current in accordance with existing regulations, had 30 years experience, with 20years in the Calgary en route specialty. He was a specialty team supervisor and worked a controller position as required. On the day of the occurrence, he reported for work at 0600 in a controller position; another supervisor was on duty. At the time of the occurrence, he was working the Alsask sector alone and performed data and controller duties. The incident occurred about 3hours before the end of his shift. Workload was described as light to moderate, with a total of five aircraft in the Alsask sector at the time of the occurrence. The controller considered himself to be well rested and without health problems. Canadian Aviation Regulation (CAR) 602.34 specifies that FL290 is an altitude reserved for eastbound aircraft unless otherwise assigned by air traffic control (ATC). FL290 was assigned to westbound ACA3697, and although it was landing in Calgary, the flight was operating in the en route airway structure. Nav Canada Air Traffic Control Manual of Operations (ATC MANOPS), section 430, provides additional guidance and limitations for controllers when assigning an altitude inappropriate for the direction of flight, including the markup of flight progress strips in a distinct and standard manner. However, the controller was not in the habit of marking the flight progress strip altitude box to indicate an aircraft flying at an altitude not appropriate for direction of flight when an aircraft was landing at an airport. Controllers are not required to indicate an altitude inappropriate for direction of flight on the radar display using an available display tool. There was no other traffic in the vicinity that required ACA3697 to be level at FL290 to maintain the required separation. No other form of separation was applied between ACA3697 and CDR8510 during the time the two aircraft were both cleared to maintain FL290. The Empress VOR is a common crossing point for eastbound and westbound traffic operating through the Alsask sector of Edmonton ACC. Since 1998, five recorded loss-of-separation incidents have occurred near the Empress VOR, with all of these incidents involving aircraft flying in opposite directions at the same altitude. Procedures had been modified in other Edmonton ACC specialties to minimize conflicts between opposite-direction traffic. TSB recommended (A00-15) that NAV CANADA commit, with a set date, to the installation and operation of an automated conflict prediction and alerting system installed at the nation's ATC facilities to reduce the risk of midair collisions. Conflict alert was implemented in the North High and Edmonton En Route specialties of the Edmonton ACC on 07July2002, and is planned for the North Low and Calgary En Route specialties by 31October2002. Functionality will be established in all national high level airspace by the end of2002.